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Biomedical subjects

L Packer

Publications and source records attributed to L Packer.

At least 487 records · Page 27Linked to original sources
PubMed1967

Ultrastructural and Photometric Evidence for Light-Induced Changes in Chloroplast Structure in vivo.

Photometric evidence for a reversible, red-light induced transmission decrease in excised leaf tissue or the thalli of certain marine algae has been obtained under conditions which correspond to the occurrence of a light-induced shrinkage of chloroplasts within the cells. Evidence supporting this conclusion is: A) The kinetics of the nonspecific transmission changes are similar to those observed in chloroplasts in vitro. B) The magnitude of the response is larger than could be accounted for by any known pigment which absorbs at 546 mmu. C) The light-induced transmission changes are optimal at pH 5.5 to 6.5 in the presence of electron flow cofactors and weak acid anions, conditions which are optimal for light-induced chloroplast shrinkage in isolated chloroplasts. D) Examination of chloroplast ultrastructure in dark incubated and illuminated chloroplasts reveals a flattening of the chloroplast structure and shrinkage.

Journal Article↗
PubMed1966

Fractionation of spinach chloroplasts by flow sedimentation--electrophoresis.

A separation of spinach chloroplasts in vitro into fractions according to size (volume) and activity (light-dependent shrinkage and NADP reduction) has been achieved by stable-flow free boundary sedimentation-electrophoresis. The salient features of this chloroplast study are: (a) separation is achieved within 30 min; (b) only small density gradients are required, thus minimizing osmotic effects; (c) the fractions are collected continuously, with size fractionation being evidenced; and (d) particles are separated into fractions of higher and lower activities as compared with the control population.

Chloroplasts↗
PubMed1965

Light-induced volume changes in spinach chloroplasts.

A light-dependent mechanism that results in a slow, high-amplitude swelling of spinach chloroplasts in vitro has been discovered. The swelling is readily observed by optical and gravimetric methods, and by the use of an electronic particle counter; all show a 100 per cent increase of chloroplast volume in the light with an approximately 10-minute half-time. The existence of an osmotic mechanism for chloroplast swelling in the dark is confirmed. The volume of illuminated chloroplasts versus NaCl concentration represents the addition of osmotic and light effects. The action of light is enhanced by electron flow cofactors, such as phenazine methosulfate (PMS). However, neither conditions for ATP hydrolysis or synthesis nor NH(4)Cl influence the time course and extent of swelling. Hence, high-amplitude chloroplast swelling is light- (or electron flow), but not energy-dependent. A remarkable inhibitory effect of inorganic phosphate on chloroplast swelling is observed in the light, but not in the dark. Another action of light on chloroplasts is known to result in a shrinkage of chloroplasts which is rapid, reversible, energy-dependent, and requires phosphate. Thus phosphate determines the action of light on chloroplast volume. Since shrinkage is reversible, but swelling is not, it may be that they reflect physiological and deteriorative processes, respectively. Chloroplasts and mitochondria appear to control their volume by similar mechanisms.

Adenosine Triphosphate↗